Merocyanine sensitized photoconductive compositions comprising zinc oxide



United States Patent 3,1105% MERQCYANENE SENSHTHZED PHGTQCGNBUC- the ultraviolet region of the spectrum, whereas the exposing source may have its maximum output in a region of the spectrum which lies within the visible region, such as an ordinary tungsten light. While various means have been previously described for sensitizing the zinc oxide TEVE C MP K QMPRISING ZENC so that it has some panchromatic or orthochromatic sen- QXKDE 5 sitivity, for example, by means of various organic dyes stewm'ta Romesmerfl fif g $0 15 such as Rose Bengal, and the like, these methods have ggi g gg Racheste? a comma Mm not been particularly satisfactory since the disadvantage Filed Aim 22, 1969, 58L 249122 of strongly dyeing thezinc oxide layer more than ofrsets 11 Claims (6L the sensitivity wh ch is supplied to the feebly sens1t1ve Zinc oxide. That 18, it is generally desirable to have some This invention relates to optically sensitized photomeans 01E seflsitilingthe OXlde Wh 1ch (1965 not P conductive layers comprising zinc oxide which are parmafienfly 601011116 Z1110 0X1d6 y which might be used' ticularly useful in making photographic copies (black and 3E final PE P Photographlc lmage- Strong hit o lor), and a method of making such photomatron of the zmc ox1de layer has an unfavorable aesconductive compositions. 15 thetrc effect and might be strongly objectionable 1n the This appficafion is a continuationimpart f my lievent that it is desired to make color prints of the origication Serial No. 630,462, filed December 26, 1956, now M1 sllblfictother unfavorable effects, Such as P abandonei trast, slow speeds, etc., are evident.

It is known that Zinc oxide can be employed i k- It is an object of my invention to provide a convenient ing nhotoconducfive layers on ordinary papgr and that means of optically sensitizing zinc oxide photoconductive photbgraphic copies can conveniently be prepared from layers in usaffll manner; l Object is to Provide these photoconductive Papers. This process has been g z g g g g g g p gg g ig l ifg ggg igi z gi z fgfgfig fii E3 object is to pr ovide a partic l ltr clas of merozy ni e Dloyed and after exposfur: of the plate to a photogrlapliigl i gg i fi g g g g e g glog ccfgggctgfi f e ggl image, eve opment o the atent image is accomp is-.e 1 1 a IS. er by means of a pigmented resinous composition which ad- 5 131 9 1? appgmm frolm Consideration of the heres to the unexposed portions of the exposed plate. owlflg P an exam? However, the xerographic plate is generally used to trans- Y mvanmfn 1S lnusmlted graphlcany the accomfer the developed image to a receiving sheet, whereas the 3 i lf dfawlng RE 1-3 are spectograms known system for using photoconductive zinc oxide gen- 3 0x156 Composltlons Sensltlzed according to y erally makes use of the zinc oxide layer itself as a means Eat prwiding1 the desired plhotographic copy witkhout transmi im gfigilggi glsgng lllgg g y (g i n f er 0 any electrostatic carge to a receiving s eet. 1 e 11 0111191156 y 0WD In In the known System f Employing Zinc Oxide in Photo 35 the art as simple rnerocyanine dyes, merocarbocyanine conductive layers, the grounded support, which is generdyes, merfdlcafbocyflme dyes, complex merocyanme filly 1paper, is first 1made SEIlSiilE/qfi to light by giving itda :22 a fgf -fizi onrileggtgamiie dyes, p ii rlalvidedbsucli an et negative e ectrostatrc c.arge on tie zinc oxi e 1 L Y Y P- 6 Car oxy layer in the substantial absence of any ultraviolet or visgroup can be attached dire/Cay to the molecule of the P ible radiation. One convenient'means of giving the zinc 40 0r carboxyl'free dyes the carboxyl group can be oxide layer an electrostatic negative charge is by means attached to molecule through an alkyl y group of ion transfer from a corona discharge. The zinc oxide Th6 merocyanlne Pelymelhme dyes useful in P photoconductive layer can then be exposed to a phot ing my invention include those dyes represented by the graphic image in the usual manner, the portions of the following general formula:

I- 1'11 O=C-N-Rg .T

zinc oxide which receive light or ultraviolet radiation loswherein R represents an alkyl group (e.g., methyl, ethyl, ing wholly, or in part (depending upon extent of expon-propyl, n-butyl, isobutyl, n-amyl, isoamyl, etc.), a hysure), the negative electrostatic charge, while the unexdroxyalkyl group (e.g., B-hydroxyethyl, y-hydroxyproposed portions of the photoconductive layer retain their pyl, etc.), an alkoxyalkyl group (e.g., B-methoxyethyl, negative electrostatic charge. The resulting latent image B-ethoxyethyl, etc.), a carboxyalkyl group (e.g., carboxycan then be developed by means of a pigmented resin 55 methyl, ,B-carooxyethyl, a-carboxyethyl, 'y-carboxypropyl, powder which has a charge opposite to the negative etc.), a sulfoalkyl group (e.g., sulfomethyl, [i-sulfoethyl, charge of the unexposed areas of the photoconductive y-sulfopropyl, fi-sulfobutyl, etc.), a carbalkoxyalkyl layer. The pigmented powder is thus firmly attached or group (e.g., carbomethoxymethyl, fi-carbomethoxyethyl, attracted to the negatively charged areas. The pigmented carbethoxymethyl, fi-carbethoxyethyl, etc.), an acyloxy- ICSlIl powder can then be afiixed to the photoconductive alkyl group (e.g., fl-acetoxyethyl, y-acetoxypropyl, etc.), layer oy simply melting the resinous vehicle at a temperan aralkyl group (e.g., benzyl, fi-phenethyl, etc.), etc., R ature below the charring temperature of the paper suprepresents a hydrogen atom, an alkyl group (e.g., methyl, ort, so that the resinous powder becomes fused to the ethyl, etc.), or an aryl group (e.g., phenyl, tolyl, etc., 'SllIr'dC of the original photoconduchve layer. Various especially a monocyclic aryl group of the benzene series), means of developing the latent image in the photocon- R represents a hydrogen atom, an alkyl group (e.g., ductive layer to a visible image have been described in methyl, ethyl, n-propyl, n-amyl, n-heptyl, etc.), a hythe priorart. droxyalkyl group (e.g., B-hydroxyethyl, 'y-hydroxypropyl,

One disadvantage in the zinc oxide normally used in etc.), a carbalkoxyalkyl group (e.g., carbethoxyrnethyl, such photoconductive layers is that the light-sensitivity fi-carbethoxyethyl, etc.), a carboxyalkyl group (e.g., carof such charged ZlHC oxide normally is at its greatest in boxymethyl, p-carboxyethyl, a-carboxyethyl, 'y-carboxypropyl, a-carboxybutyl, etc.), or an aryl group (e.g.,

' phenyl, tolyl, carboxyphenyl, sulfophenyl, etc., especially a rnonocyclic aryl group of the benzene series), X regresents an oxygen atom, a sulfur atom or a NR group wherein R represents an alkyl group (e.g., methyl, ethyl, etc.) or an aryl group (e.g., phenyl, tolyl, etc., especially a monooyclic aryl group of the benzene series), a, r: and

g each represents a positive integer of from 1 to 2, in represents a positive integer of f om 1 to 3, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from to 6 atoms in the heterocyclic ring, I represents a cyano group when Q represents a cyano group or a carbalkoxyl group (e.g., carbomethoxyl, carboethoxyl, carbobutoxyl, etc, especially such groups containing from 2 to 5 carbon atoms), or I and Q together can represent the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, which nuclei have a carbonyl group attached to the carbon atom to which I and Q are attached in the formula shown above, provided d is one when 1 represents a cyano group and Q represents a cyano group or a carbalkoxyl group.

Typical heterocyclic nuclei as defined by Z above include those of the thiazole series (e.g., thiazole, 4-methylthiazole, S-methylthiazole, 4-phenylthiazole, S-phenylthiazole, 4,5-dimethylthiazole, 4,5-diphenylthiazole, 4-(2- thienyl)thiazole, etc.), those of the benzothiazole series (e.g., benzothiazole 4-chlorobenZothiaZol-e, S-chlorobenzothiazole, 6-chlorobenzotihazole, 'l-chlorohenzothiazole, 4-methylbenzothiazole, S-methylbenzothiazole, G-rnethylbenzothiazole, S-brornobenzothiazole, 6-bromooenzothiazole, 4-phenylbenzothiazole, S-phenylbenzothiazole, 4- methoxybenzothiazole, 5 methoxybenzothiazole, 6 methoxybenzothiazole, S-iodobenzothiazole, -iodobenzothiazole, 4-ethoxybenzothiazole, 5ethoxybenzothiazole, tetrahydrobenzothiazole, 5,6 dimethoxybenzothiazole, 5,6 dioxymethylenebenzothiazole, 5 hydroxybenzotiiazole, 6 hydroxybenzothiazole, 5 carboxybenzothiazole, etc.), those of the naphthothiazole series (e.g., ec-naphthothiazole, fi-naphthothiazole, fi-rnethox -[3-naphthothiazole, 5-ethoxy-fi-naphthothiazole, 7-methoxy-a-naphthothiazolc, 8-n1etl1oXy-e-naphthothiazole, etc.), those of the thianaphtheno-7,6,4,5-thiazole series (e.g., 4-1nethoxythianapl1- theno-7, 6, 4,5-thiazole, etc.), those of the oxazole series (e.g., 4-methyloxazole, S-methyloxazole, 4-phenyloxazole, 4,5-diphenyloxazole, 4-ethyloxazole, 4,5-din1ethyloxazole, S-phenyloxazole, etc.), those of the benzoxazole series (e.g., benzoxazole, S-chlorobenzoxazole, S-phenylbenzoxazole, S-methylhenzoxazole, 6-methylbenzoxazole, 5,6 dimethylbenzoxazole, 4,6 dimethylbenzoxazole, 5- methoxybenzoxazole, 6 -n1ethoxybenzoxazole, S-ethoxybenzoxazole, 6-chlorobenzoxazole, S-hydroxybenzoxazole, 6-hydroxybenzoxazole, S-carboxybenzoxazole, etc.), those of the naphthoxazole series (e.g., ot-naphthoxazole, ,8- naphthoxazole, etc.), those of the selenazole series (e.g., 4-rnethylselenazole, 4-pi1ei1ylselenazole, etc.), those of the benzoselenazole series (e.g., benzoselenazole, S-chlorobenzoselenazole, 5-methoxybenzoselenazole, S-hydroxybenzoselenazole, tetrahydrobenzoselenazole, etc.), those of the naphthoselenazole series (e.g., cz-naphthoselenazole, fl-naphthoselenazole, etc.), those of the thiazoline series (e.g., thiazoline, 4-methylthiazoline, etc.), those of the 2-quinoline series (e.g., quinoline B-methylquinoline, S-methylquinoline, 7-rnethylquinoline, 8-rnethylquinoline, fi-chloroquinoline, S-chloroquinoline, 6-methoxyquinoline, -ethoxyquinoline, 6-hydroxyquinoline, S-hydroxyquinoline, etc.), those of the 4-quinoline series (e.g., quinoline, o-methoxyquinoline, 7-rnethylquinolinc, 8-methylquinoline, etc.), those of the l-isoquinoline series (e.g., isoquinoline, 3,4- dihydroisoquinoline, etc.), those or". the 3,3-cliallrylindolenine series (e.g., 3,3-cliinethylindolenine,

. 3,3,S-trimethylindolenine, 3,3,7-trimethylindolenine, etc.),

those of the 2-pyridine series (e.g., pyridine, S-rnethylpyridine, 4-inethylpyridine, S-methylpyridine, 6-niethylpyridine, 3,4-climethylpyridine, 3,S-dimethylpyridine, 3,6- dimethylpyridine, 4,S-dimethylpyridine, 4,6-dimcthylpyridine, 4-chloropyridine, 5-chloropyrdine, 6-chloropyridine,

- and Q of Formula 1 above comprise heterocyclic nuclei containing from 5 to 6 atoms in the heterocyclic ring, such as those of the pyrazolone series (e.g., 3-methyl-l-pheuyl- S-pyrazolone, l-phenyl-S-pyrazolone, 1-(2benzothiazolyl)-3-methyl-5-pyrazolone, etc.), those of the isoxazolone series (cg, 3-,ohenyl-5-(4H)isoxazolone, 3-methyl-5- (4H)-isoxazolone, etc), those ofthe oxindole series (e.g.,

1-alltyl-2,3-dihydro-2-oxindoles, etc.), those of the 2,4, 6-triketoor 2-thio-4,6-diketohexahydropyrimidine series (cg, barbituric acid or 2-thiobarbituric acid as Well as their l-allryl (e.g., l-rnethyl, l-ethyl, 1-n-propyl, l-nheptyl, etc.) or 1,3-dialkyl (e.g., 1,3-dimethyl, 1,3-diethyl, 1,3-di-n-propyl, 1,3-diisopropyl, 1,3-dicyclohexyl, 1,3- di(B-methoxyethyl), etc.), or 1,3-diaryl (e.g., 1,3-dip'neny1, 1,3-di(pchloropl1enyl) 1,3 -di(p-ethoxycarbonylphenyl etc.), or l-aryl (e.g., l-phenyl, l-p-chlorophenyl, 1-pethoxycarbonylphenyl), etc.) or l-alkyl-Z-aryl (e.g., lethyl-3-phenyl, 1-n-heptyl-3-phenyl, etc.) derivatives), those of the rhodanine series (i.e. 2-thi0-2,4-thiazolidinedione series), such as rhodanine, 3-alkylrhodanines (cg, 3-ethylrhodanine, 3-allyl-rnodanine, etc.), or S-arylrhodanines (e.g., 3-phenylrhodaniue, etc.), etc, those of the 2(3H)-imidazo[l,2-a]pyridone series, those of the 5,7-dioxo-6,7-dihydro-S-thiazolo[3,2-a]pyriinidine series (e.g., 5,7-dioxo-3phenyl-6,7-dihydro-5- thiazolo[3,2-a] pyrimidine, etc.), those of the 2-thio-2,4- onazolidinedione series (i.e., those of the 2-thio-2,4(3l-l, 5H)-oxazoletlioue series) (eg. 3-ethyl-2-thio-2,4-oxazolidinedione, etc.), those of the thianaphthenone series (e.g., 3(2l-l)-thianaphthenone, etc.), those of the 2-thio-2,5- .thiazolidinedione series (i.e., the 2-thio-2,5(3H,4H)- thiazoledione series) (e.g., 3-ethyl-2-thio-2,S-thiazolidinedione, etc.) those of the 2,4-thiazolidinedione series (e.g., 2,4-thiazolidinedione, 3-ethyl-2,4-thiazolidinedione, 3- phenyl 2,4 thiazolidinedione, 3-ot-naphthyl-2,4-thiazolidinedione, etc.), those of the thiazolidinone series (ea, 4-thiazolidinone, 3 ethyl 4 thiazolidinone, 3-phenyl4- thiazolidinone, 3-ot-naphthyll-thiazolidinone, etc.), those of the 4-thiazolinone series (e.g., 2-ethylrnercapto-4-thiazolinone, 2-alkylphenylainino-4-thiazolinones, Z-diphenylarnino-4-thiazolinone, etc.), those of the 2-irnino-2,4- oxazolinone (i.e., pseudohydantoin) series, those of the 2,4-i1nidazolinedione (hydantoin) series (e.g., 2,4-iniidazoline lione, 3-ethyl-2,4-irnidazolinedione, 3phenyl-2,4- imidazolinedione, 3-a-naphthyl-2,4-imidazolinedione, 1,3-

. diethyl-2,4--imidazolinedione, 1ethyl-3-u-naphthyl-2,4-irnidazolinedione, l,3-diphenyl-Z,4-irnidazolinedione, etc.), those of the Z-thio-2,4-irnidazolinedione (i.e., Z-Ihi hydantoin) series (e.g., Z-thio-Z,4-iniidazolinedione, 3-ethyl- 2-thio-2,4-irnidazolinedione, 3-phenyl2-thio-2,4-inidazolinedione, 3-ce-naphthyl-2-thio-2,4-irniclazolinedione, 1,3- diethyl 2 thio-2,4-imidazolinedione, l-ethyl-3-phenyl-2- -thio,2,4-irnidazolinedione, lethyl-3-a-naphthyl-2-thio-2,4

irnidazolinedione, 1,3 diphenyl Z-thio-2,4-imidazolinedione, etc.), those of the S-imidazolinone series (e.g., 2-npropylrnercapto-S-irnidazolinone, etc.), as Well as heterocyclic nuclei containing a sulfone group, such as those described in US. 'Paterlt 2,748,114 (e.g., 4-thiazolidone- 1,1 dioxide, 3(2H)-thianaphthenone-1,1-dioxide, etc.)

(especially a hetero-cyclic nucleus containing 5 atoms in the heterocyclic ring, 3 of said'atoms being carbon atoms, 1 of said atoms being a nitrogen atom, and 1 of said atoms being selected from the group consisting of a nitrogen atom, an oxygen atom, and a sulfur atom). 0f course, it is to he understood that the dyes useful in my invention contain at least one free carboxyl group attached to a carbon atom of the dyes depicted by Formula I.

The carboxyl-substituted dyes of my invention are markedly superior to the carboxyl-free dyes, as hereinafter shown. Dyes containing a carboxyethyl group have been found to be particularly useful.

Among the most useful dyes in practicing my invention are merocarbocyanine dyes containing at least one free carboxyl group. These dyes can advantageously be represented by the following general formula:

wherein R, R n,

above, X represents an oxygen atom or a sulfur atom and R represents an alkyl or substituted alkyl group, such as those listed above under R, or alternatively R represents an aryl group (e.g., phenyl, tolyl, etc.). Particularly useful dyes include those wherein R represents a carboxyalkyl or carboxyaryl group (e.g., carboxyrnethyl, ,B-carboxyethyl, carboxybutyl, mor p-carboxyphenyl, etc.).

Many of these merocarbocyanine dyes have excellent sensitizing action in the green and/or red regions of the spectrum.

Merocyanine or polymethine dyes useful in practicing my invention include the following:

(1 3 carboxymethyl (3 ethyl 2(3H) benzothiazolylidene -rhodanine (2) 3 B carboxyethyl 2 benzothiazoline (3) 3 carboxymethyl benzothiazoline (4) 3 carboxyrnethyl 5 [(3 methyl 2(3H) thiazolinylidene isopropylidene] rhodanine (5) 3 ethyl 5 [(3 carboxymethyl zoxazolylidene) -ethylidene] rhodanine (6) 3 carboxymethyl 5 [(3 ethyl 2(31-1) Zoxazolylidene) -ethylidene] rhodanine (7) 3 carboxymethyl 5 [(3 ethyl 2(3H) benzothiazolylidene -ethylidene] rhodanine (8) 2 (3 carboxymethyl 4 oxo 2 thiono 5- thiazolidylidene -3 -ethyl-5- (3 -cthyl-2 (3H) -benzoxazolylidene ethylidene] -4-thiazolidone (9) 3 carboxy 4 [(3 ethyl 2(3H) benzothiazolylidene -ethylidene] -5-pyrazolone 10) 5- 3-{3-carboxyethyl-2 3H) -benzoxazolylidene) 2,4-hexadienylidene]-1,3-diphenylbarbituric acid 11) 4-[3-canboxyethyl-2-(3H) -benzoxazolylidene) butenylidene]-3-phenyl-2-isoxazolin-5-one (12) 4- (3-carboXyethy1-2 3H) -benzoxazolylidene) -2,4-.

hexadienylidene] -3 -phenyl-2-isoxazolin-5 -one 13) 4-[ (3-B-oarboxyethyl-2 3H) benzoxazolylidene) ethylidene] -3-phenyl-2-isoxazolin-S-one (14) 1-carboxymethyl-5-[ (3-ethyl-2(3H)-benzoxazo1ylidene) -ethylidene-3-phenyl-2-thiobarbituric acid 15 3-caIboxymethyl-5-( 1-methyl-2( 1H) -pyridy-lidene) rhodanine 16) 3-canboxymethyl-5- 3-ethoxycarbonylniethyl- 2 3H) -thiazolinylidene isopropylidene] rhod anine (17) 5-[ (3-car-boxyethyl-2- 3H) -thiazolinylidene) ethylidene] -3 -carb oxymethylrhodanine (18) 5-(1,8-carboXyethyl-4(1H)-pyridylidene)-3-ethylrhodanine (3,3 dicyanoallylidene) 2 (3,3 dicyanoallylidene) 2(3H) benben- - 19 2- 3 -earboxy-methyl-4-0xo-2-thio-5 -thiazolidinylidene) -3-ethyl-5 [(1-ethyl-2( 1H) -naphtho[ 1,2]thiazo1- ylidene -1-phcnylethylidene] -4-thiazolidinone (20) 5 (5 -carboXy-3 -methyl-2 3H) -benzoxazolylidene ethylidene] -2,4-thiazolidinedione (21) 5- 3-,B-carboXyethyl-2 3H) -benzothiazolylidene) ethylidene] -2,4-thiazolidinedione (22) 5- 1 -o-carboxyphenyl-2; 3-ethyl-2 3H) -b enzothiazolylidene)ethylidene] -3-ethylrhodanine (23) 5- 3-0-carboxyphenyl-4- 3-ethyl-2 3H) -benzothia'- v zolylidene) -but-3 -enylidene] -3 -ethoxycanbonylrnethylrhodanine Z and X each have the values given (24) 5-[1-o-oarboxypheny1-2-(5-chloro-3-ethyl-2-(3H)- benzothiazolylidene ethylidene] -3 -ethoxycarbonylmethylrhodanine (25 5 1-o-carboxyphenyl-2- 3-ethyl-2( 3H) -benz0thiazolylidene ethylidene] -3 -ethoxycanbonylmethylrhodanine v (26) 5- l-(4-carboxybutyl)-5,6-dich1loro-3-ethyl- 2 3H) -benzimidazolylidene ethylidene] -3ethylrhodanine Methods for making the above nierocyanine or polymethine dyes have been previously described in the prior art. Among the patents describing the preparation of such dyes are the following:

US. 2,493,747 issued on January 10, 1950 US. 2,493,748 issued on January 10, 1950 U.S. 2,519,001 issued on August 15, 1950 US. 2,526,632 issued on October 24, 1950 US. 2,778,822 issued on January 22, 1957 British 450,958 issued on July 15, 1936 Other patents showing such dyes include Knott U.S. Patent 2,728,766, issued December 27, 1955 and Brooker US. Patent 2,454,629, issued November 23, 1948. Merocyanine dyes containing a oanboxyl group attached to the benzene ring of a heterocyclic nucleus can be prepared by reacting the carboxyl-substituted cyclammonium qu-aternary salts of Firestine U.S. Patents 2,609,371, issued September 2, 1952 and 2,647,057, issued July 28, 1953, with a D ains et a1. type intermediate according to methods Well known to those skilled in the art.

The above opticalsensitizing dyes can be combined with.

the zinc oxide photoconductive material in any convenient manner. For example, the optical sensitizing dye can be added to the zinc oxide composition while dissolved in an organic solvent. Pyridine, methanol, ethanol, acetone, etc, can be used to dissolve many of the merocyanine dyes useful in practicing my invention. The zinc oxide can be uniformly dispersed in an organic solution of the binder customarily employed for the zinc oxide and a solution of the nierocyanine dye added to this coating solution. After thorough mixing, the sensitized solution can be coated on a paper support and dried in the usual manner.

Alternatively, an unsensitized zinc oxide coating can be prepared as described above and after removal of the organic solvent, the paper coating can be immersed in a solution (organic or aqueous) of the merocy-anine dye. This method has been found to be particularly useful in that higher speeds can be frequently obtained.

The binders for the zinc oxide comprise many of the resinous compositions which are commercially available. Such resins are sold under trade names, such as Plaskon ST 856, Rezyl 405-18, Pliolite S-7, Styresol 4440, DC 804, etc. These resins comprise styrene-butadiene copolyrners, silicone resins, styrene-alkyd resins, silicone-alkyd resins, soya-alkyd resins, polyvinyl chloride, polyvinyl acetate, etc. The methods of making such resins have been previously described in the prior art. For example, styrene alkyd resins can be prepared according to the method described in US. Patent 2,361,019, issued October 24, 1944; US. Patent 2,258,423, issued October 7, 1941; US. Patent 2,453,665, issued November 9, 1948, etc. Other binders, such as paraffin, mineral waxes, etc., can also be employed. These binders are generally characterlzed as having marked hydrophobic properties (i.e., being Lubstantially free of any water-solubilizing groups, such as hydroxyl, free acid groups, amide groups, etc.) and as being good electrical insulators or as having high electrical resistivity. These binders can be easily dissolved in organic solvents having a boiling point below the eh-arring temperature of the paper support. Also, these binders have the desirable property of readily dispersing the zinc oxide photoconductive material. Some resinous binders are relatively poor insulators and do not provide coatings which can be stored for prolonged periods of times after the photoconductive coatings have been negatively charged. This is particularly noticeable at rela-v tively high humidities, and th photoconductive coatings should be negatively charged shortly before use in such instances, that is, it is not advisable to charge the photo conductive coatings too long in advance before use. Such problems are Well understood y those skilled in the art. Nonpolar solvents have been found to be particularly useful in preparing the photoconductive layers in that any residual solvent which cannot be removed does not have a deleterious efifect on the keeping qualities of the photoconductive layers. Such solvents include the aromatic hydrocarbons, such as benzene, xylencs, toluene, etc.

The zine oxide photoconductive material employed in my invention should generally consist of relatively small particles of less than 0.5 micron mean diameter. Such zinc oxide materials are readily available and can be purchased under a variety of trade names, such as Protox No. 168 (New Jersey Zinc Company), etc. Sufficient binder should be employed to insulate each of the zinc oxide particles from the surrounding particles in the composition. The most useful or optimum quantity of zine oxide to binder for a particular binder can be readily determined by making a series of test coatings wherein the quantity and relative amounts of zinc oxide to binder are employed. Exposure of the charged photoconductive layer to visible radiation or ultraviolet radiation causes a loss or reduction of the negative charge in those portions of the photo-conductive material which are exposed to the radiation. The degree of loss will depend on the intensit and time of exposure to the radiation, in general. The resulting latent electrophotographic image can then be developed to a visible image in a variety of ways, including those which have been previously employed in electrophotographic processes, such as xerography. A particularly useful means of developing the latent electrop hotographic image comprises use of a magnetic brush. This magnetic brush development makes use of a ferromagnetic powder, such as iron filings, which has been intimately mixed with pigmented resin, or sulfur. Agitation of the ferromagnetic powder and pigmented resin results in a triboelectric'eifect wherein the pigmented resin acquires an electric charge depending upon the relative position of the resin to the ferromagnetic powder in the triboelectric series. That is, ordinary iron powder is below most resins in the triooelectric series, and mixture with a resin higher in the series results in the deposition of a positive electrostatic charge on the resin. The resulting mixture can then he picked up by a magnet on which the iron particles, or other ferromagnetic powder, arrange themselves in the conventional pattern, so that the long chains of filings resemble an ordinary brush. This magnetic brush can then be placed in contact with the exposed photoconductive layer and the brush passed across the negative electrostatic latent image which is on the surface of the photoconductive material. As the magnetic brush passes over the areas of the photoconductive material which have residual negative charge thereon, the electrostatic attraction between the charged pigmented resin particles and the oppositely charged image areas in the photo-conductive material is greater than the attraction between these particles and the ferromagnetic powder, so that the pigmented resin is deposited on the surface of the photoconductive material roughly in proportion to the residual charge on the surface of the photoconductive layer. By selecting a resin with a low melting point, the developed image can then be fixed to the surface of the paper by heating to a temperature above the melting point of the resin, but below the c wing temperature of the paper. The resin in the pigmented resin compositions can be varied, dependinr upon the effects desired and the type of copy which is being reproduced. Such resins may be the same as those employed in the insulating layer coated on the paper support, such as styrene-butadiene resin, etc. The particle size of the pigmented resin used in development can vary, although the range of 0.1 to 25 microns is adequate for most purposes. Various pigments can be used in the resin developing compositions. The ability of the pigmented resin to accept a positive charge is dependent upon the type of resin selected. The pigment merely serves to impart color to the resin and probably imparts very little, if any, influence on the overall charge of the pigmented resin.

The following examples will serve to illustrate the manner of using the optically sensitized photoconductive materials of my invention.

EXAMPLE mg. of 3-ethyl-5-[(3)-carboxymethyl-2GED-benzoxazolylidene)ethylidenelrhodanine were dissolved in 126 cc. of methanol containing a trace of triethylamine to facilitate dissolving of the dye. There were then added 60 g. of zinc oxide (Florence White Seal No. 7, New Jersey Zinc Company) and the mixture stirred for 30 seconds in a Waring Blender. The resulting slurry was filtered and the treated zinc oxide filter cake was again placed in the Waring Blendor along with another 126 ml. portion of methanol and stirred for 30 seconds. The slurry was again filtered and the dyed zinc oxide filter cake was broken up and allowed to dry in the air. A mixture of 50 of the treated zinc oxide, 18.2 g. of Plaskon ST-856 (Allied Chemical & Dye Corp.) a silicone-alkyd resin), and 51.8 g. of xylene was placed in Waring Blendorfor 30 minutes: The resulting viscous mixture or dope of zinc oxide was coated on a glossy, singlewveight *baryta coated paper stock at a coverage of approximately 5 g./ft. The coated paper was then charged under a corona discharge and exposed for one-half second in a sensitometer to tungsten illumination. The exposed coating was then developed by the magnetic brush technique described above using small iron particles and black pigmented sulfur. Finally, the image was. fixed by fusing the black pigmented sulfur to the paper surface by applying heat. A duplicate coating was treated in the same manner, with the sensitizing dye being omitted, this coating serving as a control.

The electrical characteristics of the control and dye- -treated coatings with respect to initial charge and dark decay were essentially the same. However, the s, sort of the dye-treated coating was approximately twenty times that of the coating containing no sensitizing dye.

As mentioned above, the merocyanine dyes of my invention can be combined with the zinc oxide by simply dipping the coated surface of zinc oxide into a solution of the merocyanine dye. This solution can be an aqueous solution or a solution in an organic solvent, depending upon the solubility characteristics of the particular dye. Methanol, pyridine, benzene, etc. are suitable solvents for many of the dyes of my invention.

In a manner similar to that described above, a number of merocyanine dyes were used to sensitize previously coated zinc oxide by the dip technique. The results of such sensitization are given below, together with the result obtained for a coating which was not treated with any merocyanine dye. The untreated sample is identified as the control.

in the manner illustrated above, other carboxyl-sublarly useful in practicing my invention.

stituted dyes were used to sensitize photoconductive elements comprising 'a relatively thin layer of photoconductive zinc oxide. The following table (Table II) illustrates the speed increase afforded by using the carboxylsubstituted dyes of my invention. The dyes were incorporated in the photoconductive elements by immersing the photoconductive elements in a solution containingdye in the concentration shown in the table. Where a combination of solvents was used to obtain solution, a small amount of dye (e.g., 2 mg.) was wet with a small amount of the first solvent containing a rather large amount of the second named solvent. The requisite amount of the second solvent was then added to complete solution (or in some cases, the dye was dissolved in a small amount of the first solvent alone and a much larger amount of the second solvent added). The immersed samples were then thoroughly dried and exposed in an intensity scale sensitometer to tungsten illumination and in a spectrograph. The relative white light speeds of theexposed coatings are shown in the table after development of the exposed sample by means of the magnetic brush technique described above.

Where the sensitizing dye has its maximum absorption in the blue region of the spectrum, an exposing source other than tungsten illumination, which has its maximum output in the blue region of the spectrum, is recommended. For example, fluorescent lamps have their maximum output in the blue and ultra-violet regions of the spectrum.

Table II Relative Dye Control. 9

MeH=methanoL NEt =triethylamine.

Acet=aeetone.

Ocp=0-chl0rophenol.

The dyes of our invention can be used in the form containing free carboxyl groups, or as salts (e.g., triethylamine, sodium, pyridine, etc.) of such carboxyl group. The term carboxyl as used herein means either COOH or a salt of this radical (e.g., alkali metal, organic amine, ammonium). I

In a manner similar to that described above, other merocyanine dyes can be used to sensitize photoconductive zinc oxide compositions either by mixing the dye with the zinc oxide prior to coating, or by the immersion technique described above. In some instances, there is a material increase in the range of spectral sensitivity of the photoconductive zinc oxide compositions with a concomitant increase in speed. In order to extend the sensitivity to longer wavelengths, sensitizing dyes containing a polymethine chain of several units can be employed. For example, the sensitivity can be extended to longer Wavelengths using such dyes as 3-(p-carboxyphenyl)-5- [(3 ethyl 2(3H) benzoxazolylidene)-2-butenylidene] rhodanine, 3-carboxymethyl-5 (3 -ethyl-2 3 H -benzoxazolylidene)-2-butenylidene]rhodanine, etc.

Merocyanine dyes containing a carboxyrnethyl or a ,8- carboxyethyl group attached to one of the nitrogen atoms of the heterocyclic nuclei have been found to be particu- As indicated above, the merocyanine dyes useful in practicing my invention can beprepared according to techniques well known to those skilled in theart. Two basic methods of preparation can be used to advantage. One method comprises reacting a cyclammonium qua- 1 0 ternary salt containing in a reactive position an acetylated aminovinyl-, butadienyl or hexatrienyl group with a ketomethylene compound containing no substituent in the reactive methylene position. A second method comprises US. 2,693,472 issued November 2, 1954 Brit. 674,003 issued June 18, 1952 Brit. 681,738 issued October 29, 1952 Brit. 704,770 issued March 3, 1954 Brit. 704,840 issued March 3, 1954 French 1,112,494 issued November 16, 1955 The following examples will serve to illustrate the preparation of two open-chain merocyanine dyes which are useful in practicing my invention.

EXAMPLE A 3 B carboxyethyl 2-(3,3-dicyanoallylidene)benzothiazoline (dye 3) was obtained when 3.49 g. of 3-,8-carboxyethyl-2-methyl-benzothiazolium iodide, 3.3 g. of malononitrile, 2.9 g. of ethyl orthoformate and 2.02 g. of triethylamine were heated together in 15 ml. of pyridine solution for 10 minutes. After chilling the reaction mixture, the dye was collected on a filter and washed with methyl alcohol. The yield of dye was 32% crude and 20%, in two crops, after two recrystallizations from methyl alcohol. The red crystals lost solvent at about 205 C. and then melted at 216217 C. with decomposition.

Dye 9 above was prepared by condensing 2-fi-acetanilidovinyl-3-ethyl-2(3H)-benzothiazolium iodide with 3- carboxy-S-pyrazolone in the presence of triethylamine.

EXAMPLE B 3 carboxymethyl-2-(3,3-dicyanoaliylidene)benzothiazoline (dye 4) was obtained when 2.88 g. of 3-carboxymethyl-Zanethylbenzothiazolium bromide, 3.3 g. of ma-lonenitrile, 2.9 g. of ethyl orthoformate, and 2.02 g. of triethylamine were heated together in 15 ml. of pyridine solution for 10 minutes. The cool reaction mixture was stirred with 200 ml. of ether. After chilling the mixture, the dye was collected on a filter. The yield of dye was 34% crude and 13% after two recrystallizations from methyl alcohol. The orange needles melted at 221222 C. with decomposition.

The accompanying drawing illustrates schematically the increased spectral range of sensitivity provided by three of the dyes useful in practicing my invention. In FIG- URES 1, 2 and 3, the solid curves show the range of sensitivity as Well as the region of maximum sensitivity. Exposures were made in a spectrograph in the usual manner using tungsten illumination.

In ElGU RE 1, the solid curve represents the sensitivity of a photoconductive element comprising a relatively thin layer of photoconductive zinc oxide sensitized with 3- carboxy 4 [(3-cthyl-2(3H)-benzothiazolyli-dene)ethylidene]-5-pyrazolone. The relative speed of this coating corresponds to that of dye 9 in Table II.

In FIGURE 2, the solidourve represents the sensitivity of a pho-toconductive element comprising a relatively thin layer of photoconductive zinc oxide sensitized avith 5-[(5- carboxy-3-methyl-2 3H) benzoxazolylidene) ethylidene] 2,4-t-hiazolidinedione. The speed value for this coating corresponds to that of dye 20 in Table II above.

in FIGURE 3, the-solid curve represents the sensitivity of a photoconductive element comprising a relat-ively thin layer of photoconductive zinc oxide sensitized with 3-carfor this coating correspon s to ab ve.

It has been found that the dyes of my invention containing a free carboXyl group have a markedly improved sensitizing action toward no oxide as compared with the corresponding dyes containing no free carboxyl group. This appears to be true regardless of the manner by which the carboxyl group is attached to the molecule of the sensitizing dye. vention, the carboxyl-containing dyes are characterized consistently by increased speeds as compared with dyes containing no free carbon l group. In silver halide photography, the carbonyl and carbonyl-free dyes frequently have about the same sensitizing efiiciency. This is illustrated in the following two tables. In these tables, the coatings were prepared by the mixin" technique described in above Example and the coatings were then dried, exposed, and developed by the magnetic brush technique described. The results obtained are summarized below.

B=3 ethyl 5 [(3 ethyl 2(311) benzothiazolylidone) c-thylidene] rhollanine.

3 ethyl 5 [(3 ethyl 2(31-1) benzoxazolylidene) ethylidcne] rhodaninc.

The invention has been descri'ed in detail particular reference to preferred embodiments thereof, but it will be understood that vari ions and modifications can be effected within the spirit and scope or" the invention as described hereinabove and as defined in the appended claims.

What I claim and desire secured by Letters Patent of the United States of America l. A photoconductive composition comprising photoconduct-ivc zinc oxide, a high dielectric insulator for said zinc oxide, and a merocyranine dye selected from those re resented by the following general formula:

the class consisting of an oxygen atom, a sulfur atom and a NR group wherein R represents a member selected from the class consisting of an alkyl group and an aryl group, n, q and d eacn represents a positive integer of In the compositions of the present infrom 1 to 2, in represents a po s e of from 1 to 3, Z represents the non-metallic atoms necessary to to a hcterocyc-lic nucleus selected from the class g of those of the thiazole series, those of the thiazole series, those of the naphthothiazole series, those of the thianaphtheno7,6,4,5-thiazolc series, those of xazole series, those of the bcnzor-zazole series, those of the nap loxazole series, those of the selenazole series, those of the benzoselenazole series, those of the naphthaselenazole series, those of the t-liiazoline series, those of the Z-q oline series, those of the 4-quinoiine series, those the l-isoquinoline series, those of the 3,3-dialkylindoleninc seric those of the Z- yridine series and those of the 4-pyridine series, I represents a member selected the class cons' ting of a cyano group and the atoms ation with Q ne essary to complete a heteroring selected from the class consisting of those of idi edione series, those of the 2,4-thiazolidinethe c t 2,5-thiazo 'azolinone series, those of the 2-imino-2,4-oxazolinone series, those of the 2,4-imidazolinedione series, those of the Z-thio-2,4-imidazolinedione series, and those of the 5- imidazolinone series, Q, when I represents a cyano group, represents a member selected from the class consisting of a cyano group and a carbalkoxyl group, provided :1 represents one when 1 represents a cyano group and Q repr cents a member selected from the class consisting of a cyano group and la carbalhoxyl group, and provided furthcr that said merc-cyanine dye contains at least one carbonyl group attached to a carbon atom thereof.

A photoconductive composition comprising photoconductive zinc oxide, a high dielectric insulator for said zinc oxide and, 3-fi-carbox ethyl 2 (3,3 dicyanoallyli re)benzotniazoiinc.

J. A photoconductive composition comprising photo- J-I Q zinc oxide and, 4-[S-carboxycthyl-Z(3H)-benzoxazolylidene butenylidene] -3 -phenyl-:2-isoXaz0lin-5 -one.

'7. A photoconductive composition of claim 1 containing a merocyanine dye represented by the structural formula in which n represents the integer 1, 121 represents the integer 1, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus of the henzothiazole series, and when Q and J are combined, they form a hcteroc clic nucleus of the rhodanine series.

8. A photoconductivc composition of claim 1 containing a merocyanine dye represented by the structural form a in which n represents the integer l, m represents the integer l, Z represents the non-metallic atoms necessary to co. etc a lie-crocyclic nucleus of the thiazoline series,

and when Q and J are combined, they form a heterocyclic nucleus of the rhodanine series.

9. A photoconductive composition of claim 1 containing a merocyanine dye represented by the structural formula in which n represents the integer 1, 111 represents the integer 1, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus of the benzoxazole series, and when Q and J are combined, they form a heterocyclic nucleus of the rhodam'ne series.

10. A photoconductive composition of claim 1 containing a merocyanine dye represented by the structural formula in which n represents the integer l, m represents the integer 1, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus of the benzothiazole series, and when Q and J are combined, they form a heterocyclic nucleus of the pyrazolone series.

11. A photoconductive composition of claim 1 containing a merocyanine dye represented by the structural formula in which n represents the integer 1, m represents the integer 1, Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus of the benzoxazole series, and when Q and I are combined, they form a heterocyclic nucleus of the isox azolone series.

References Cited in the file of this patent UNITED STATES PATENTS 1,730,505 Hart Oct. 8, 1929 2,493,747 Brooker et a1. Jan. 10, 1950 2,493,748 Brooker et al Jan. 10, 1950 2,638,473 'Edwards May 12, 1953 2,685,509 Doyle Aug. 3, 1954 3,052,540 Grieg Sept. 4, 1962 FOREIGN PATENTS 538,610 Belgium June 15, 1955 201,416 Australia Apr. 13, 1956 OTHER REFERENCES Chemical Abstracts, 43, 734%, 1949.*

Chemical Abstracts, 45, 501 8e, 1951.*

Young et al.: R.C.A. Review, vol. XV, No. 4, pages 469-484, 1954* Mees: The Theory of the Photographic Process, Re-

20 vised edition, pp. 483-493, MacMillan Co., N.Y. (1954) Nelson: Journal of the Optical Society of America, 46, No. 1, Jan. 1956, pages 13-16.*

* Copy in Sci. Library. 

1. A PHOTOCONDUCTIVE COMPOSITION COMPRISING PHOTOCONDUCTIVE ZINC OXDIE, A HIGH DIELECTRIC INSULATOR FOR SAID ZINC OXIDE, AND A MEROCYANINE DYE SELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 